Modify Unity search, to be less invasive

Unity shortcuts and workspaces

By default, ALT opens the HUD, which can be useful, but not as much as to require such a simple shortcut: it will be
changed to CTRL + ALT + SPACE.

Also by default, SUPER opens the launcher. Used to Spotlight in OsX, I prefer using Super+Space for this. In
addition, having SUPER reserved to the launcher,
it means that Super+1 will open the first icon in the launcher, Super+2 the second one, etc. I prefer using these
shortcuts to select workspaces